1. Field of the Invention
The present invention generally relates to electrophotographic devices and methods for adjusting a print used therein, and more particularly to serial-type electrophotographic devices and methods for adjusting a print used therein in which the quality of image formed is improved by the adjustment.
2. Description of the Prior Art
Currently, there is a demand for economic and small-size electrophotographic devices. Thus, a serial-type electrophotographic printer in which an electrophotographic unit is mounted in a carriage, for printing, has been developed. In this type of electrophotographic printer, an image is transcribed on recording paper by a carriage being conveyed in a perpendicular direction to a feeding direction of the recording paper. The transcribed image is fixed by a photographic fixing device provided in the feeding direction of the recording paper. In this type of electrophotographic printer, an improvement in the quality of the recorded image is desired.
FIG. 1A is a partial plan view of a conventional serial-type electrophotographic printer and FIG. 1B is a sectional view showing a carriage thereof.
A serial-type electrophotographic printer 11 shown in FIGS. 1A, 1B is disclosed in Japanese Laid-Open Patent Application No. 61-152463. In the serial-type electrophotographic printer 11, feeding rollers 13a, 13b for feeding recording paper 12 and a shaft 14 parallel to the feeding rollers 13a, 13b are provided. A removable carriage 15, guided by the shaft 14, is provided in a perpendicular direction to a feeding direction of the recording paper 12. The carriage 15 is conveyed by a driving motor (not shown). At a downstream side in the feeding direction of the recording paper 12, a photographic fixing device 16, which is longer than the width of the recording paper 12, is provided. Also, a transcription device 17 is provided under the recording paper 12 in the feeding direction of the recording paper 12.
A drum 21 which rotates at a speed in response to movement of the carriage 15 is mounted in the carriage 15. A surface of the drum 21 is uniformly charged and an electrostatic latent image is formed thereon. The electrostatic latent image is made into a visible toner image by toner 24 in a developer 25. The toner being applied by a developing roller 26. The toner image is transcribed to the recording paper 12 by the transcription device 17 which faces the drum 21 on the opposite side of the recording paper 12. The transcribed portion is photographically fixed by the photographic fixing portion 16.
In this serial-type electrophotographic device 11, feeding of the recording paper is an intermittent action. Accordingly, part of an image quality fixed when the recording paper is being fed is different from that when the recording paper is stopped. It prevents a uniform fixing quality from being conducted. For example, a part of the recording paper in contact with the fixing roller when the fixing roller is stopped has a glossy appearance.
In order to solve the above problem, a serial-type electrophotographic device has been developed in which a photographic fixing roller is provided in a carriage.
FIG. 2 is a schematic illustration showing a carriage in which a photographic fixing device is provided. A carriage 15 having a photographic fixing device 27 in FIG. 2 is disclosed in Japanese Laid-Open Utility Model Application No. 61-145649. In the carriage 15, a cleaner 30 is provided in order to remove toner particles remaining on the drum 21 after a printing cycle.
In the photographic fixing device 27, a photographic fixing roller 28 is provided which rotates in the same direction as the drum 21. In the photographic fixing roller 28, a heat source 29 (i.e. a halogen lamp) is provided. The photographic fixing roller 28 is heated by the heat source 29 before a printing operation and the temperature thereof is detected and controlled by a temperature sensor (not shown) such as a thermistor. That is, the photographic fixing device 27 is conveyed with the drum 21 in order to conduct the photographic fixing subsequent to the transcription of the image.
Since the transcription by the transcription device 17 is conducted by applying a prescribed electric voltage between the transcription device 17 and the drum 21, an electrically conductive material, such as electrically conductive gum is applied on the baseboard in the photographic fixing device 17.
In the serial-type electrophotographic printer, the photographic fixing roller operates at approximately 180.degree. C. Since the toner 25 is fixed on the recording paper, water retained in the recording paper is vaporized and shrinks the recording paper.
FIGS. 3A, 3B and 3C are schematic illustrations describing a problem of the conventional serial-type electrophotographic printer. In FIG. 3A, each image line of width A L1, L2 . . . is printed continuously at a proper temperature at a proper humidity.
When the recording paper is shrunk by heat applied by the photographic fixing roller 28, a width of each line L1, L2 . . . becomes B and gaps C which prevent each line from being arranged continuously are formed, as shown in FIG. 3B. In this case, the quality of the image is deteriorated.
Also, when the gap C is expected and the amount of recording paper fed is reduced, each line L1, L2 . . . is overlapped because of the change of water-absorption due to a change of temperature and humidity. In this case also, the quality of the image is deteriorated.